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    Subject[PATCH v2 1/3] serial: core: Potential overflow of frame_time
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    From: VAMSHI GAJJELA <vamshigajjela@google.com>

    uart_update_timeout() sets a u64 value to an unsigned int frame_time.
    While it can be cast to u32 before assignment, there's a specific case
    where frame_time is cast to u64. Since frame_time consistently
    participates in u64 arithmetic, its data type is converted to u64 to
    eliminate the need for explicit casting.

    Signed-off-by: VAMSHI GAJJELA <vamshigajjela@google.com>
    ---
    v2:
    - use DIV64_U64_ROUND_UP with frame_time

    drivers/tty/serial/8250/8250_port.c | 2 +-
    include/linux/serial_core.h | 4 ++--
    2 files changed, 3 insertions(+), 3 deletions(-)

    diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
    index 141627370aab..d1bf794498c4 100644
    --- a/drivers/tty/serial/8250/8250_port.c
    +++ b/drivers/tty/serial/8250/8250_port.c
    @@ -1510,7 +1510,7 @@ static inline void __stop_tx(struct uart_8250_port *p)
    * rather than after it is fully sent.
    * Roughly estimate 1 extra bit here with / 7.
    */
    - stop_delay = p->port.frame_time + DIV_ROUND_UP(p->port.frame_time, 7);
    + stop_delay = p->port.frame_time + DIV64_U64_ROUND_UP(p->port.frame_time, 7);
    }

    __stop_tx_rs485(p, stop_delay);
    diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
    index bb6f073bc159..b128513b009a 100644
    --- a/include/linux/serial_core.h
    +++ b/include/linux/serial_core.h
    @@ -558,7 +558,7 @@ struct uart_port {

    bool hw_stopped; /* sw-assisted CTS flow state */
    unsigned int mctrl; /* current modem ctrl settings */
    - unsigned int frame_time; /* frame timing in ns */
    + unsigned long frame_time; /* frame timing in ns */
    unsigned int type; /* port type */
    const struct uart_ops *ops;
    unsigned int custom_divisor;
    @@ -764,7 +764,7 @@ unsigned int uart_get_divisor(struct uart_port *port, unsigned int baud);
    */
    static inline unsigned long uart_fifo_timeout(struct uart_port *port)
    {
    - u64 fifo_timeout = (u64)READ_ONCE(port->frame_time) * port->fifosize;
    + u64 fifo_timeout = READ_ONCE(port->frame_time) * port->fifosize;

    /* Add .02 seconds of slop */
    fifo_timeout += 20 * NSEC_PER_MSEC;
    --
    2.42.0.655.g421f12c284-goog
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